The field of the invention relates generally to air conditioning system control coordinated with engine control.
Vehicles are typically equipped with an air conditioning system to provide cabin cooling and to dry air for dehumidifying functions. Air conditioning systems typically include a compressor driven by a vehicle""s internal combustion engine. The compressor can be either engaged, fully or partially, or disengaged to the engine via an electronically controlled clutch.
During air conditioning system operation under certain operating conditions, the compressor cycles between an engaged and disengaged state. Cycling is typically controlled based on refrigerant pressure in the air conditioning system. When the engine and clutch are coupled, pressure decreases and significantly cooled cabin air is circulated through the vehicle. Such operation continues until pressure reaches a minimum value where the clutch is controlled to disengage the engine and compressor. If air circulation is continued, pressure increases until it reaches a maximum value. At this maximum value, the compressor is then re-engaged via the clutch and cycling repeats.
It is also known to disengage the engine and compressor during vehicle launch conditions, thereby allowing more engine output. In this way, degraded vehicle launch performance is avoided, even when air conditioning is operational. Vehicle launch is determined based on vehicle speed, throttle position, and various other factors.
The inventors herein have recognized disadvantages with the above approaches. First, driver comfort is degraded during clutch engagements during some driving conditions. In other words, during some driving conditions, clutch engagements are felt strongly by vehicle operators and comfort is therefore degraded. Second, optimum fuel economy is not obtained since compressor cycling engagement is not coordinated to vehicle and engine operating conditions. In other words, during some conditions, extra fuel is added to the engine to provide air conditioning while maintaining engine output at a desired level. During other conditions, no extra fuel is needed to provide air conditioning.
An object of the present invention is to provide methods for controlling engagements of an air conditioning compressor coupled to an internal combustion engine capable of improving fuel economy and/or improving drive feel.
The above object is achieved and disadvantages of prior approaches overcome by a control method for use with an internal combustion engine and an accessory device, the engine and device coupled to a vehicle, the method comprising: determining when the device is cycling between an engaged state where the engine is coupled to the device and a disengaged state where the engine is de-coupled from the device; and engaging the device based at least on an operating condition when the device is disengaged.
By engaging the device in response to an operating condition when the device is cycling between an engaged state and a disengaged, it is possible to coordinate cycling of the device with current driving conditions. In other words, rather than asynchronous operation between various control systems, the present invention provides a method to couple device cycling control to other conditions.
An advantage of the above aspect of the invention is that improved fuel economy is achieved.
Another advantage of the above aspect of the invention is that improved drive feel is achieved. In another aspect of the invention, the above object is achieved and disadvantages of prior approaches overcome by a control method for use with an internal combustion engine and an air conditioning compressor, the engine and compressor coupled to a vehicle, the method comprising: indicating a transient vehicle driving condition while the vehicle moving; estimating a duration of a cycle in which the device is engaged and disengaged due to an air conditioning system parameter; and engaging the compressor in response to said indication when said duration is greater than a predetermined duration.
By coordinating engagement with a transient vehicle driving condition while the vehicle moving, it is possible to engage the compressor unbeknownst to the vehicle driver. Further, by performing engagement when a percentage disengaged duration is greater than a predetermined duration, it is possible to prevent excessive compressor cycling.
An advantage of the above aspect of the invention is that improved drive feel and improved customer satisfaction is achieved.
In yet another aspect of the invention, the above object is achieved and disadvantages of prior approaches overcome by an article of manufacture comprising a computer storage medium having a computer program encoded therein for use with an internal combustion engine and an air conditioning compressor, the engine and device coupled to a vehicle having brakes. The computer storage medium comprises code for determining when the compressor is cycling between an engaged state where the engine is coupled to the compressor and a disengaged state where the engine is de-coupled from the compressor, code for indicating when the brakes are actuated, code for estimating a percentage disengaged duration of a cycle in which the compressor is engaged and disengaged due to an air conditioning system parameter, and code engaging the compressor based at least on said indication when said percentage disengaged duration is greater than a predetermined value.
By engaging the compressor in response to brake actuation when a percentage disengaged duration is greater than a predetermined value, it is sometimes possible to operate the compressor without added fuel to the engine since kinetic energy from the vehicle can be used to power the compressor. In other words, this added coordination between compressor cycling control and vehicle braking conditions provides more opportunities to operate the compressor without excess fuel to the engine.
An advantage of the above aspect of the invention is that improved fuel economy is achieved.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.